2003-01-14 21:32:45 +01:00
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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2003-05-21 01:21:38 +02:00
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2003-01-14 21:32:45 +01:00
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<meta http-equiv="Content-Type"
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content="text/html; charset=windows-1252">
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<title>Shorewall NAT</title>
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2003-05-21 01:21:38 +02:00
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2003-01-14 21:32:45 +01:00
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<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
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2003-01-14 21:32:45 +01:00
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<meta name="ProgId" content="FrontPage.Editor.Document">
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</head>
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<body>
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<blockquote>
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<table border="0" cellpadding="0" cellspacing="0"
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style="border-collapse: collapse;" width="100%" id="AutoNumber1"
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bgcolor="#400169" height="90">
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<tbody>
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<td width="100%">
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<h1 align="center"><font color="#ffffff">Static NAT</font></h1>
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</td>
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</tr>
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</tbody>
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</table>
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<p><font color="#ff0000"><b>IMPORTANT: If all you want to do is forward
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ports to servers behind your firewall, you do NOT want to use static
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NAT. Port forwarding can be accomplished with simple entries in the
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<a href="Documentation.htm#Rules">rules file</a>.</b></font></p>
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<p>Static NAT is a way to make systems behind a firewall and configured
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with private IP addresses (those reserved for private use in RFC1918)
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appear to have public IP addresses. Before you try to use this technique,
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I strongly recommend that you read the <a
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href="shorewall_setup_guide.htm">Shorewall Setup Guide.</a></p>
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<p>The following figure represents a static NAT environment.</p>
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<p align="center"><strong> <img src="images/staticnat.png"
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width="435" height="397">
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</strong></p>
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<blockquote> </blockquote>
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<p align="left">Static NAT can be used to make the systems with the 10.1.1.*
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addresses appear to be on the upper (130.252.100.*) subnet. If we assume
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that the interface to the upper subnet is eth0, then the following /etc/shorewall/NAT
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file would make the lower left-hand system appear to have IP address
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130.252.100.18 and the right-hand one to have IP address 130.252.100.19.</p>
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<table border="2" cellpadding="2" style="border-collapse: collapse;">
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<tbody>
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<tr>
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<td><b>EXTERNAL</b></td>
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<td><b>INTERFACE</b></td>
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<td><b>INTERNAL</b></td>
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<td><b>ALL INTERFACES</b></td>
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<td><b>LOCAL</b></td>
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</tr>
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<tr>
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<td>130.252.100.18</td>
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<td>eth0</td>
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<td>10.1.1.2</td>
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<td>yes</td>
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<td>yes</td>
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</tr>
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<tr>
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<td>130.252.100.19</td>
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<td>eth0</td>
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<td>10.1.1.3</td>
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<td>yes</td>
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<td>yes</td>
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</tr>
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</tbody>
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</table>
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<p>Be sure that the internal system(s) (10.1.1.2 and 10.1.1.3 in the above
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example) is (are) not included in any specification in /etc/shorewall/masq
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or /etc/shorewall/proxyarp.</p>
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<p><a name="AllInterFaces"></a>Note 1: The "ALL INTERFACES" column is used
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to specify whether access to the external IP from all firewall interfaces
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should undergo NAT (Yes or yes) or if only access from the interface in
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the INTERFACE column should undergo NAT. If you leave this column empty,
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"Yes" is assumed.<2E>The ALL INTERFACES column was added in version 1.1.6.</p>
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<p>Note 2: Shorewall will automatically add the external address to the
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specified interface unless you specify <a
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href="Documentation.htm#Aliases">ADD_IP_ALIASES</a>="no" (or "No") in
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/etc/shorewall/shorewall.conf; If you do not set ADD_IP_ALIASES or if
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you set it to "Yes" or "yes" then you must NOT configure your own alias(es).
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<b>RESTRICTION: </b>Shorewall can only add external addresses to an interface
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that is configured with a single subnetwork -- if your external interface
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has addresses in more than one subnetwork, Shorewall can only add addresses
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to the first one.</p>
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<p><a name="LocalPackets"></a>Note 3: The contents of the "LOCAL" column
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determine whether packets originating on the firewall itself and destined
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for the EXTERNAL address are redirected to the internal ADDRESS. If this
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column contains "yes" or "Yes" (and the ALL INTERFACES COLUMN also contains
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"Yes" or "yes") then such packets are redirected; otherwise, such packets
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are not redirected. The LOCAL column was added in version 1.1.8.</p>
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</blockquote>
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<blockquote> </blockquote>
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<p><font size="2">Last updated 4/11/2003 - </font><font size="2"> <a
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href="support.htm">Tom Eastep</a></font> </p>
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<a href="copyright.htm"><font size="2">Copyright</font> <20> <font
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size="2">2001, 2002, 2003 Thomas M. Eastep.</font></a><br>
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<br>
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</body>
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</html>
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